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In the room I stayed I had a problem with air flow. Even when door and windows closed, a little bit of air still flows and that make me sick especially on winters.

So I want to detect this air flow with a cheap system. I looked for some airflow sensors but I it looked to me not so suitable for my reason. One of the ideas that come to my mind is using Infrared Thermometer and make an image of the room. The places where air flows should be cooler then other sides.

What are you opinions, what kind of system can be used for this reason?

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closed as too broad by Adam Davis, markrages Sep 1 at 20:00

There are either too many possible answers, or good answers would be too long for this format. Please add details to narrow the answer set or to isolate an issue that can be answered in a few paragraphs.If this question can be reworded to fit the rules in the help center, please edit the question.

    
Just wondering...whether proper heating could avoid this headache instead of a complicated air flow detection system ? –  Plutonium smuggler Aug 31 at 19:04
    
The room has already proper heating system. But even though the room is heated well, if some kind of breezes exists in room and you are sensitive enough, then you catch a cold. (the apartment I stayed is built after to the top of the building, so it wasn't build very well) –  cheour Aug 31 at 19:18
    
Low tech measurement tool: talcum (or baby) powder. Spray a tiny bit in the air where you suspect a draft and see if the dust is blown away. –  jippie Aug 31 at 19:41
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I believe it is a fallacy that draughts cause colds there may be some other mechanism causing your sickness, for example fungal exposure. I suffered for several months while living in Texas. Once diagnosed I was cured completely quite quickly. –  gbulmer Aug 31 at 19:46
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First you can't catch a cold from cold air. Colds are caused by viruses. Second, do you really want a room with no air circulation? Stale air can cause more physical problems than a little bit of cold air. –  Barry Aug 31 at 22:13

6 Answers 6

In the room I stayed I had a problem with air flow. Even when door and windows closed, a little bit of air still flows

This is normal. All residential rooms need some airflow. A completely sealed room will have severe moisture and mold problems. Plus you will be dead by morning on account of breathing all the available oxygen.

and that make me sick especially on winters.

No, it didn't. You got sick because you were exposed to a virus somewhere. Probably an elevator.

So I want to detect this air flow with a cheap system. One of the ideas that come to my mind is using Infrared Thermometer and make an image of the room. The places where air flows should be cooler then other sides.

Maybe. IR thermometers will detect several-degree differences and usually not from air.

For a cheap system, get some tape and a roll of toilet paper. Attach 50cm strips to the ceiling and watch it move.

If you determine that you have a strong draft ("airflow" is normal, "draft" is unwanted air movement) from a window, have the building owner repair the seals. This is an easy and cheap job. If the draft is coming from corners or gaps between the wall panels your only option is to move.

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I'd personally say most of this answer could go into the comment section. The other answers answer the question directly, in a manner that helps anyone looking for a way to do this, rather than making observations on the asker's situation. And some of the observations are going way too far on the limited information the asker has given (like "No, it didn't. You got sick because you were exposed to a virus somewhere. Probably an elevator." and "This is an easy and cheap job. If the draft is coming from corners or gaps between the wall panels your only option is to move." –  Assorted Trailmix Sep 1 at 13:47

What you are looking for is called an anemometer, a common device used to detect airflow is called the hot-wire anemometer from Wikipedia:

Hot wire anemometers use a very fine wire (on the order of several micrometres) electrically heated up to some temperature above the ambient. Air flowing past the wire has a cooling effect on the wire. As the electrical resistance of most metals is dependent upon the temperature of the metal (tungsten is a popular choice for hot-wires), a relationship can be obtained between the resistance of the wire and the flow speed.

It seems like you could design something to resistance in a fairly straightforward manner, the article goes on to discuss various signal capture methods.

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The OP specifically asked for a cheap system. Hot-wire anemometry is not cheap. I work in a lab that uses them all the time. Hot wires cost a few hundred dollars each and are extremely fragile. The actual anemometer is probably an order of magnitude more expensive that the hot wire. This of course assumes that you buy commercially available products. You could do hot-wire anemometry much cheaper if you make the sensors and anemometers yourself but that would definitely not be a weekend project. –  OSE Sep 1 at 15:55
    
Yes, my post is to give a name for what the OP is asking for. There are methods to do home-made hot-wire anemometry which a Google search (or academic paper search) would turn up. Many involve breaking open a light bulb and using the filament as a sensing element. –  Zuofu Sep 1 at 17:25

Why would flowing air be cooler than still air? In order to cool anything, it has to evaporate moisture from that "anything"'s surface. I don't think a thermometer will tell you much.

You can detect slight breezes easily with smoke or steam, though, or often with a candle flame. Try moving a cup of water fresh from the teapot around the room, especially if you can cast light upon the steam rising from the cup so you can see its flow. That's just about the cheapest test you can perform - you probably already own 100% of your equipment & materials.

If you don't have a teapot, use your coffeemaker... and if you don't have a coffeemaker, use the hottest water you can get from the hottest faucet in the house.

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Well smart idea, I'll give it a chance :) –  cheour Aug 31 at 19:15
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If the outside air is cooler than inside, then the IR camera will show the cool air places. –  George Herold Aug 31 at 19:15

Here's a suggestion: make an appliance with two NTC thermistors, fairly close but not too close to each other -- say 10 cm/4 inches away so that they're exposed to the same temperature, but don't influence each other.

The first one should be biased with a low current, either from a constant-current source or a resistive divider. Either way, you should use the lowest current that is practical to measure with around 0.5 degree Celsius/1 degree Fahrenheit accuracy -- I'm certainly talking sub-mA here, probably in the range of 10s of uA. This avoids any kind of self-heating effect.

The second one should be biased with a constant current source that is a bit higher -- you should size it according to your NTC's R25 parameter, thermal resistance, etc. I estimate 5 to 10 mA should work for an NTC with R25 = 10kΩ. This will significantly self-heat the second NTC, but after a quick transient period it should settle to a temperature that's X degrees above ambient, where the exact value of X depends on all factors mentioned; you're shooting for a fairly high value, but not too high to risk exceeding the NTC's rated temperature. If X is not high enough, it's going to be hard distinguishing between a gentle breeze and random fluctuations.

Start by measuring X in an environment with still air. The effect of a breeze on the second NTC is to lower its thermal resistance, or in other words, reduce X. Whether the breeze is colder, hotter or the same temperature as ambient doesn't matter, because the first NTC is measuring the change in temperature due to the breeze. The point is to compare the difference between the temperature reported by the second and the first NTC. In still air it should always hover around X, but in case of a breeze, it should be detectably lower than X. The stronger the breeze, the more X will decrease.

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Isn't this how MAFs in an automobile generally work? –  SplinterReality Sep 1 at 1:59

You can do this with a Wheatstone bridge that has an NTC thermistor as on each of the two sides . You have to pick the resistance and drive voltage so the thermistors self- heats. Any air currents in any direction will cool the thermistor slightly and increase the voltage across it. A sensitivity of a tiny fraction of a degree is possible. You keep one thermistor shielded from air flows and the other one exposed.

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This is what's known as an XY problem.

You assume that air flow ("drafts") are what is making you sick. That's nonsense, and an old wive's tale.

As others have pointed out, airflow is required to maintain a healthy environment. At the extreme case, you'd suffocate due to lack of oxygen. With too low air flow your living space would tend to get too humid and you'd have mold problems. You'd also accumulate toxins from things like cooking fumes, off-gassing of plastics, cleaning products, etc.

You need decent air flow and air exchange in order to avoid a "sick building." That's more likely to make you sick than too much air flow. (Sick buildings often caused by poor air flow than by too much air flow.) Google "sick building syndrome" to learn more...

You've gotten some good advice from better minds than mine on how to measure air flow, but it won't solve your problem.

Returning now from a discussion of why this isn't an EE problem to actual discussions of electronics...

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